Contoured supersonic nozzle

ABSTRACT

A convergent-divergent nozzle for supersonic expansion of turbine motive fluid is presented wherein the major part of contouring of the flow paths between adjacent nozzles is in the direction between top and bottom walls between adjacent nozzle side walls, the contouring being accomplished by contoured top and bottom nozzle walls which are asymmetrically contoured in an axial direction to define a symmetric flow path therebetween.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.362,402 filed May 21, 1973, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the field of nozzles for turbo-machinery. Moreparticularly, this invention relates to the field ofconvergent-divergent nozzle structure for the creation and expansion ofsupersonic flow of a compressible fluid for turbine motive fluid.

Converging-diverging nozzles are needed to create and expand asupersonic stream (a pressure ratio exceeding approximately 1.85) totransform a high energy stream into a high velocity jet with goodefficiency and minimal shock, flow separation or jet deflection.

Conventional prior art nozzles for convergent-divergent supersonicexpansion are of two general types. One type has convergent-divergentprofiles machined into opposed side surfaces or side walls of adjacentnozzles so as to define, in one dimension, convergent-divergent passagesbetween these profiled side surfaces. The top and bottom surfaces ofsuch passages are parallel to each other to define a constant height forthe convergent-divergent passage, or the height may vary linearlybetween nozzle inlet and exit. The other type of conventional nozzle isin the form of rounded nozzle passages, as used in drilled and reamednozzle blocks. The passages machined into these nozzle blocks may becircular in cross-section and thus two-dimensionallyconvergent-divergent. In any case, the contours of the nozzle passages,including convergence, divergence and throat location, are not definedby the inner and outer circumferential walls of the nozzle passage;rather, they are defined either by the contouring between the side wallsin the nozzle or by the uniform annular variations of the drilled andreamed passages.

Both of these prior art nozzle configurations, i.e., those in which theconverging, throat and diverging sections, are defined either by spacingbetween contoured adjacent side walls of nozzle elements or by thecircumferential changes in the drilled and reamed passages, arecharacterized by several problems and disadvantages of long standing inthe art. Cost is a particular problem in that precise machining must beemployed to achieve the desired side wall contours where the passagesare being defined by the contours between adjacent side walls; and,similarly, expensive drilling and reaming is involved for the drilledand reamed devices. In addition, the entire unit can be rendered uselessby a mistake in the machining of other forming operations, andtolerances are particularly critical.

Another particular problem is that these prior art devices presentdistinct limitations in regard to flow capacity. In the round nozzles,for example, increased capacity is achieved by enlarging the contouredcircular passages, thus also increasing the overall size of the unit.Assuming that the nozzles are arrayed in a circumferential array forcommunication with a turbine wheel, an attempt to increase capacityinvariably results in enlargement of the overall size of theturbo-machinery beyond merely a diameter change, a result which is oftenvery undesirable or which may result in excessive tip speeds. Similarly,if the nozzle arrays are associated with a radial turbine rather than anaxial turbine, the increased size of the nozzle array required forincreased flow capacity results in a disproportioning in size betweenthe nozzle unit and the turbine wheel and may lead to inefficientdelivery of motive fluid to the turbine wheel.

SUMMARY OF THE INVENTION

For the sake of clarity in discussing the invention herein, it will beunderstood that the term "nozzle" is a structural and functional elementwith a flow passage defined by a pair of adjacent side walls and opposedtop and bottom walls. Relating that terminology to the prior art, thecontouring to accomplish convergence, throat definition and divergencehas been accomplished by curved and relatively complex contouring of theadjacent side walls of individual nozzles so that adjacent side wallsconverge with respect to each other to a point of minimum separation andthen diverge with respect to each other, the plane of minimum separationdefining the throat. The opposed top and bottom walls are typicallyparallel to each other.

By way of major distinction, in the primary embodiment of the presentinvention the adjacent side walls are regular throughout most or all oftheir length and the definition of the throat in the nozzle as well asthe definition of the converging and diverging portions of the nozzlepassage are defined primarily by contouring both of the opposed top andbottom walls which may be full or partial rings. The word "regular" asused herein and in the claims means that the side walls are flatsurfaced straight or curved elements, as distinguished from contouredwalls which serve to vary the flow path therebetween. Stated in anotherway, adjacent side walls are parallel to each other (includingequidistantly spaced curved surfaces) when viewed as a flat developedsection of the nozzle ring or when used as a radial section with respectto the turbine axis. The contouring of both of the opposed top andbottom walls may be easily accomplished by simple turning on a lathe orby sheet metal forming, as distinguished from the very complex threedimensional machining of the side walls as has previously been requiredwith the situation wherein nozzle contouring was defined betweenadjacent side walls. However, the contouring of the opposed top andbottom walls must be such that top and bottom walls present asymmetrical flow passage between the top and bottom walls downstream ofthe throat in the direction of gas flow. Bearing in mind that thenozzles are in an annular array, compensation must be made for theannular curvature in order to achieve a symmetric flow passage in thedirection of gas flow; accordingly, contouring of the top and bottomwalls downstream of the throat is nonsymmetrical, the asymmetry being afunction of the annular curvature of the nozzle array. This contouringof the top and bottom walls makes it possible to locate or relocate thethroat of the nozzle merely by interchanging pieces of metal ofdifferent angular or curved shapes and permits an accommodation of wideflow ranges merely by removing the top and bottom surfaces andsubstituting top and bottom surfaces of different angular or curvedshapes. All of this can be accomplished without in any way disturbingthe adjacent side walls of the nozzle passages. This invention, mostimportantly, also makes possible the use of simple sheet metal elementsto form the side walls of supersonic nozzle passages, and these sheetmetal elements can be standard elements which are easily bent or formedto take on a desired shape; this being in significant contrast to theprior art wherein these adjacent side wall components had to beprecisely and intricately machined in three dimensions. Furthermore, asindicated above, wide changes in flow rates, pressure ratios, Machnumber and other performancee parameters and characteristics can beaccomplished and accommodated merely by substitution of top and bottomwall elements of different angular or curved shapes and sizes.

The asymmetrical contouring of the top and bottom walls of the nozzledownstream of the throat occurs in the axial direction, i.e. in a radialplane which includes the axis of the turbine. This asymmetricalcontouring in the axial plane produces a symmetrical flow passagebetween the top and bottom walls of the nozzle in the direction of gasflow, thus providing for desired shockwave interaction to producebalanced flow conditions. This asymmetrical contouring of the top andbottom walls downstream of the throat to produce a symmetrical flowpassage is a most important feature of the present invention whichdistinguishes this invention over the patent to Angell U.S. Pat. No.2,910,005 where it has been suggested to contour just the inner wall ofa nozzle passage, thus creating a nonsymmetrical flow passage.

The throat of the nozzle of the present invention, i.e. the plane ofsmallest cross-sectional area, is determined by the contouring of thetop and bottom walls of the nozzle rather than by complex contouring ofthe side walls. The throat may be perpendicular to the flow passage, orit may be arranged at any desired angle to the flow passage. Inaddition, if desired, a part of the adjacent nozzle side walls can becurved so as to cooperate with the contouring of the top and bottomwalls in defining the location of the throat. However, in such anarrangement the contours of the top and side walls are still the majorfactor, i.e. contribute greater than 50% in determining the location ofthe throat and defining the convergent and divergent sections of thenozzle.

A point of major importance to note in connection with the presentinvention is that since the location of the throat is defined bycontouring of the top and bottom walls of the nozzle passage, thelocation and/or size of the throat and hence the area ratio of thenozzle can be changed at will merely by substitution of a different topand bottom wall element. Thus, it becomes possible to form nozzle arrayshaving standard and inexpensive sheet metal elements defining adjacentside walls, and these standard nozzle arrays can be adapted for a widerange of requirements by a proper selection of contoured top and bottomwall segments which can also be of sheet metal and which can be made tobe easily insertable and removable as units.

Accordingly, one object of the present invention is to provide a noveland improved convergent-divergent supersonic nozzle element.

Another object of the present invention is to provide a novel andimproved convergent-divergent supersonic nozzle element wherein thelocation of the throat is defined by contouring of the top and bottomwalls of the nozzle.

Still another object of the present invention is to provide a novel andimproved convergent-divergent supersonic nozzle unit wherein adjacentside walls are parallel throughout all or a large part of their lengthand wherein the nozzle throat is defined by contouring of the top andbottom walls of the nozzle unit.

Still another object of the present invention is to provide a novel andimproved convergent-divergent supersonic nozzle unit wherein thedivergent section has asymmetrical top and bottom walls in the axialdirection to define a symmetrical flow passage therebetween.

Another object of the present invention is to provide a novel andimproved supersonic nozzle unit wherein standard nozzle side wallelements can be employed and wherein the unit is adaptable for a widerange of requirements by use of differently contoured top and bottomwall elements.

Other objects and advantages of the present invention will be apparentto and understood by those skilled in the art from the followingdetailed drawings and description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, wherein like elements are numbered alikein the several figures:

FIG. 1 is a generalized partial schematic showing of a turbine nozzleunit of the present invention shown in a horizontal development with thetop walls of the nozzle elements removed;

FIG. 2 is a view along line 2--2 of FIG. 1, with the other walls 12removed to permit an unobstructed view of wall 12x, showing the nozzletop and bottom walls contoured asymmetrically;

FIG. 2A is a view along line 2A--2A of FIG. 1 showing a symmetrical flowpath defined by top and bottom walls contoured asymmetrically as in FIG.3;

FIG. 3 is a view like FIG. 2 taken along line 2--2 of FIG. 1 showing thenozzle top and bottom contoured walls without the important feature ofaxial asymmetrical contouring;

FIG. 3A is a view along line 2A--2A of FIG. 1 showing a nonsymmetricalflow path defined by top and bottom walls contoured as in FIG. 2;

FIG. 4 is a modified version similar to FIG. 1 showing partial curvedand profiled sections of the nozzle side walls. The side wall profilingaffecting only the subsonic portion of the nozzle;

FIG. 5 is a view of wall 12x along line 5--5 of FIG. 4 with the otherwalls removed to permit an unobstructed view of wall 12x;

FIG. 5A is a view along line 5A--5A of FIG. 4;

FIG. 6 is a partial side elevation view of a radial turbine according tothe present invention; and

FIG. 6A is a view along line 6A--6A of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to a combined consideration of FIGS. 1 and 2, each nozzle10 of the present invention is made up of a pair of adjacent side wall12, a bottom wall 14, and a top wall 16, the walls combining to define aflow passage 18 for the delivery of motive fluid to the buckets 20 of aturbine wheel. The nozzles 10 are arranged in an annular array about theaxis 11 of the turbine wheel. The turbine wheel forms no further part ofthis invention, and no further description is made of it herein. Itwill, however, be noted that the same principle of top and bottom wallcontouring to be described herein may also be applied to the rotatingblading of reaction turbines, to provide a supersonic expansion acrossthe rotating blades.

The side walls 12 may be made of any desirable and even simple materialsuch as sheet metal, and the discharge ends adjacent the turbine bucketsare slightly angled or contoured to form pointed or rounded ends ofsomewhat airfoil shape to minimize flow separation or shock. Theimportant point to note is that along the major length of the side walls12 from the plane of flow inlet 22 to the plane of discharge 24 the sidewalls are regular (or parallel in projection or radial section). Thus,all of the previous exotic contouring common in the prior art todetermine convergent, divergent and throat sections of individualsupersonic nozzles is not present in these side walls.

Referring now to FIG. 2, it can be seen that starting at inlet 22 topwall 16 and bottom wall 14 converge inwardly toward each other to pointsor locations 26 to form a converging section of the nozzle passage; andthe top and bottom walls then diverge away from each other to the outlet24 to form a diverging section of the nozzle passage. It is ofparticular importance to note that the invention contemplates the sidewalls 12 may be of uniform, essentially rectangular shape with the topsurface 12a as indicated in FIG. 2, rather than being specificallycontoured to conform to the shape of top and bottom walls 14 and 16.Walls 12 in height dimensions may also be of varying height to conformto the changing height between bottom wall 14 and top wall 16. Top andbottom walls 16 and 14 may each be circular rings (preferably machinedto provide the desired contouring) with slots to receive side walls 12;or the top and bottom walls may be a plurality of individual segments(which may be contoured sheet metal elements) between each adjacent pairof side walls. Bearing in mind that adjacent walls 12 are regular withno special contouring therebetween, it will be immediately seen that theplane defined between top and bottom walls 16 and 14 at points 26defines the narrowest cross-section of the passage of flow passage 18,i.e. defines the throat 28. Throat 28 is, of course, only conceptual inthat it is the location of the narrowest cross-section of thepassageway, and thus it is indicated in phantom in FIG. 2. Expansiondownstream of the throat occurs primarily in the direction between thetop and bottom walls 16 and 14 rather than between adjacent side walls12.

Turning now to a combined consideration of FIGS. 2 and 3, FIG. 3 shows apassage contour which is symmetric in an axial plane (i.e. a plane whichincludes the turbine axis and extends radially through the nozzleannulus) generating a cylindrical vortex. The configuration shown inFIG. 3 generates a gas flow passage or gas path as indicated by thesolid lines in FIG. 3A, this gas flow path being a tangentially curvedpath in order to conform to the curvature of the nozzle annulus. Thedesired contour is a symmetrical flow or gas path downstream of thethroat 28. The curved and nonsymmetrical path of FIG. 3A resulting fromthe axially symmetric configuration of FIG. 3, although being a possibleconfiguration for the present invention, is not the preferredconfiguration because it results in considerable thermodynamicdisadvantages because the supersonic gas flowing in the nozzle is forcedinto a tangentially curved path. The resulting shockwaves and expansionwaves and secondary flow patterns resulting from the curvature are knownto cause serious efficiency losses and possibly choking of the flowpassages because exit velocity, pressure and temperature are verydifferent from the desired values.

The configuration of FIG. 2 and the resulting gas flow passage of FIG.2A eliminate the problems associated with the FIGS. 3 and 3Aconfiguration. The contours of top and bottom walls 16 and 14 downstreamof the throat in the FIG. 2 configuration are asymmetrical in the axialplane, the asymmetry being in an amount sufficient to compensate for theeffect of the annular curvature of the nozzle annulus so that thesymmetrical flow path of FIG. 2A is generated between the top and bottomwalls 16 and 14. In other words, the gas flow passage, or the flow pathseen by the supersonic gas, downstream of the throat 28 is symmetricalbetween walls 14 and 16 about line X, line X also representing thedirection of flow and coinciding with line 2A--2A of FIG. 1. In thismanner the supersonic gas flow is directed through the nozzle and intothe rotor blading in a path which is perfectly symmetrical between thetop and bottom walls, and supersonic expansion occurs between the topand bottom walls 16 and 14. Efficient supersonic expansion of the gasdepends upon the symmetry configuration achieved in the gas path of FIG.2A so that the top and bottom walls reflect the shockwaves in a propermanner to meet and interact at the flow passage center line X.Conventional prior art designs which depend on the contouring of theside walls for nozzle profiling can not avoid the effects of annularcurvature of the nozzle annulus and thus can not achieve the symmetryrealized by the present invention.

If for any design consideration whatsoever it becomes desirable ornecessary to change the dimension or location of the throat, walls 14and 16 can be replaced. For example, referring both to FIGS. 2 and 3,walls 14 and 16 are shown as being detachably connected to inner andouter shrouds 30 and 32. Walls 14 and 16 could be replaced merely bydetaching them from the shrouds and replacing them with walls havingcontours indicated at 14' and 16', in which event the intersectionpoints 26' would locate throat 28' at a different position in the throatchannel and with a significantly different size. Since side walls 12 maybe of uniform shape and size, and since the top and bottom walls 16 and14 may be individual segments located and housed between adjacent sidewalls or rings with grooves to receive the side walls, the location andshape of the top and bottom walls, and thus the location and size of thenozzle throat, can be changed without any modification or changewhatsoever in the side walls. This means that the side walls can be ofsimple material such as sheet material airfoil shapes and can bepermanently installed in the nozzle wheel, thus creating a nozzle wheelwhich can be varied for a wide range of applications merely by changingtop and bottom walls which define the nozzle passages.

Referring now to FIGS. 4, 5 and 5A, views similar to FIGS. 1, 2 and 2Aare shown with one modification. That one modification is that theupstream bends of the adjacent nozzle walls 12 have curved and/orprofiled sections 34 upstream of the throat plane 28. The side wallsegments 12 may still be formed of simple sheet metal elements withthese curved or profiled upstream end portions 34 being either integralwith walls 12 or separate attached pieces. However, by incorporation ofthese curved or profiled upstream end portions the height between lowerand upper walls 14 and 16 may remain constant, i.e., as shown in FIG. 5walls 14 and 16 may be parallel where they are coextensive with thecurved or profiled end sections 34, and the flow passages will still beconverging between end sections 34 because of the shape between adjacentend sections. The side walls in this configuration are regulardownstream of the throat 28 and divergence is accomplished as in FIG. 2and FIG. 3 by divergence of the bottom and top walls 14 and 16 away fromeach other. The divergence of the walls 14 and 16 is preferablyasymmetrical in the axial plane shown in FIG. 5 to produce thesymmetrical flow path downstream of the throat as shown in FIG. 5A. Ofcourse, in the configuration of FIGS. 4 and 5 the top and bottom walls16 and 14 upstream of the throat can also be inclined toward each other(as shown in dotted lines in FIG. 5) so that the relative inclination ofthese walls would also contribute to the definition of the convergingportion of the flow passages. Thus, by providing the curved upstream endportions 34 of the adjacent side walls the convergent part of the nozzlepassage can be defined either by the relationship between the sidewalls, or by a combination of the relationship between the side wallsand the relationship between the top and bottom walls. The dotted lineconfiguration of FIG. 5 also shows variation in location and size of thethroat 28' by substitution of top and bottom walls 16' and 14'.

It is to be noted that by selection or adjustment of the geometry ofwalls 16 and 14 the gas flow discharging from the nozzles can be in theform of a circular cylinder or a converging or diverging cylinder. Thus,the contour and direction of the gas path can be selected and developedsuch as is shown in FIGS. 1, 2 and 2A so as to make the axial componentof the gas enter the rotor blading in a direction parallel to the rotoraxis. Similarly, by selecting and developing the direction and shape ofthe gas path as shown in FIGS. 4, 5 and 5A, the gas can be made to exitthe nozzle annulus and enter the blading in a conical pattern whichconverges toward or diverges away from the rotor axis. It is importantto note that such changes in flow pattern can be obtained by simplychanging the top and bottom walls to appropriate shapes for the desiredend result, but without changing or affecting the side walls 12.Especially when considered in conjunction with the variability of throatarea and area ratio which can be accomplished with the presentinvention, this means that such changes and adjustments can be made toexisting equipment and that the resulting flexibility of design achievedby the present invention can be used for purposes of cost reduction andstandardization of equipment which must presently be custom engineeredand individually manufactured.

It is also to be noted that by appropriate configuration of the top andbottom walls in conjunction with the selection of the flow path thelocation of the throat 28 in each nozzle may be staggered from nozzle tonozzle (as shown in FIG. 1), or the location of throat may be in acommon plane in each nozzle (as shown in FIG. 4) whereby what may betermed a throat line is generated which is circumferential andtangential with respect to the nozzle annulus. No such circumferentialand tangential throat line is now known in the prior art.

An important point to note is that the ability of the present inventionto define the converging and diverging portions of the nozzle passagesin the height of the passages rather than in the width of the passagesbetween the side walls as in prior art, makes it possible to designsymmetrical flow passages of extremely high volume capacity but of shortlength from inlet to outlet. This factor is of extreme important ininstallations where very high flow volumes are needed but where spacerequirements would otherwise limit the size of the machinery and thusprevent realization of the desired flow capacity. For example the gaspath of FIG. 5A which results from the contours shown in FIG. 5, isknown as a "sharp-edged supersonic nozzle of minimum length", and itdepends for efficient operation on the symmetry of the gas pathresulting from the contours of FIG. 5 which are a function of andcompensate for the curvature of the annular nozzle ring.

The principles of the present invention, particularly the contouring ofthe inner and outer walls, can be applied to any apparatus where asupersonic gas stream is desired. FIGS. 6 and 6A shows these principlesapplied to a radial turbine 40. Radial turbine 40 has an array ofcontoured vane elements 42 which are pivotally mounted on posts 44 toprovide an adjustable vane configuration. The vanes constitute the sidewalls of the nozzles in the context of the terminology of the presentinvention. The nozzle passages 18 are defined by adjacent vanes 42 andby opposed top and bottom or outer and inner walls 16 and 14 which arecontoured as desired to define the nozzle throat 28 and the divergentflow passage downstream of the throat from which the supersonic flow isdelivered to the buckets 20.

The ability to incorporate an adjustable vane arrangement in asupersonic machine is a significant improvement over conventionaldesigns. Adjustable stator blades are common for subsonic apparatus, butprior art technology using contoured nozzle side wall profiles to definea throat and divergent passage does not accommodate adjustment by vanerotation in supersonic apparatus since the rotation would disturb thepassage symmetry which is essential for efficient supersonic expansion.In the present invention distortion of passage symmetry is avoidedbecause the supersonic expansion occurs in a direction perpendicular tothe plane of movement of the side wall vanes.

Adjustment of the vanes may be by manual setting or may be continuouslyvariable by controls in conventional manners. A first setting of thevanes is shown in the solid lines in FIG. 6A, and a second setting isdepicted by the dashed line configuration with prime superscriptsindicating dimensions in the second configuration. The adjustabilityfeature not only allows variation of throat width (defined as t and t')and exit width (defined as X and X') but it also permits variation ofthe area ratio A*/A (where A* equals throat area and A equals exit area)and hence pressure ratio. This is so because the vane geometry and pointof rotation can be selected so as to complement the geometry of theprofiled walls 14 and 16 in such a manner as to vary the width of theoriginal throat 28 as a fixed or variable relationship of exit width X,both being a function of angular nozzle position. In the position shownin the dashed lines in FIG. 6A, the area ratio would be a maximum, beingdominated by the contours of walls 16 and 14. Changing the vanes intothe position shown in the solid lines, throat area would be onlyslightly reduced while exit area would be reduced by about 25%. Hence,the area ratio would be reduced by approximately 25%. It is important tonote that the capability of incorporating adjustable vanes in asupersonic configuration produces the capability of varying area ratio,and not just exit area; conventional subsonic designs vary only exitarea since they incorporate no throat.

While a preferred embodiment has been shown and described, variousmodifications and substitutions can be made thereto without departingfrom the spirit and scope of the invention. Accordingly, this inventionhas been described by way of illustration and not limitation.

What is claimed is:
 1. A convergent-divergent nozzle including:a pair ofopposed spaced apart side walls; a top wall extending between said sidewalls; and a bottom wall spaced from said top wall and extending betweensaid side walls; said top and bottom walls and said side wallscooperating to define a flow passageway; and said top and bottom wallsbeing contoured to cooperate with each other to define at least thethroat of the nozzle and a divergent section downstream of the throat,said contouring of said top and bottom walls defining a symmetric flowpassage therebetween in the direction of flow downstream of said throat.2. A convergent-divergent nozzle as in claim 1 wherein:said contouringof said top and bottom walls is the major factor in defining saidthroat.
 3. A convergent-divergent nozzle as in claim 1 wherein:saidopposed side walls are regular throughout the major part of theirlength.
 4. A convergent-divergent nozzle as in claim 1 wherein:the angleof said throat with respect to the direction of flow in the nozzledownstream of the throat is a function of the contouring of said top andbottom walls.
 5. A convergent-divergent nozzle as in claim 1wherein:said side walls are of uniform size and shape.
 6. Aconvergent-divergent nozzle as in claim 1 wherein:said contoured wall isdetachably connected to support means whereby said contoured walls arereplaceable with walls of different contour to change the definition ofthe throat of the nozzle and the divergent section of the nozzle.
 7. Aconvergent-divergent nozzle as in claim 1 wherein:said top and bottomwalls are contoured to also define the convergent section of the nozzle.8. An array of convergent-divergent nozzles about an axis for deliveryof motive fluid to a turbine, each of said nozzles including:a pair ofopposed spaced apart side walls; a top wall extending between said sidewalls; and a bottom wall spaced from said top wall and extending betweensaid side walls; said top and bottom walls and said side wallscooperating to define a flow passageway; and said top and bottom wallsbeing contoured to define at least the throat of the nozzle and thedivergent section of the nozzle, said contouring of said top and bottomwalls of each nozzle being asymmetric with respect to said axis anddefining a symmetric flow passage between said top and bottom walls inthe direction of flow downstream of said throat.
 9. An array ofconvergent-divergent nozzle as in claim 8 wherein:said contouring ofsaid top and bottom walls in each nozzle is the major factor in definingsaid throat.
 10. An array of convergent-divergent nozzles as in claim 8wherein:said opposed side walls of each nozzle are regular throughoutthe major part of their length.
 11. An array of convergent-divergentnozzles as in claim 8 wherein:the angle of said throat with respect tothe direction of flow in the nozzle downstream of the throat is afunction of the contouring of said top and bottom walls.
 12. An array ofconvergent-divergent nozzles as in claim 8 wherein:said side walls ofeach nozzle are of uniform size and shape.
 13. An array ofconvergent-divergent nozzles as in claim 8 wherein:said contoured wallsof each nozzle are detachably connected to support means whereby saidcontoured walls are replaceable with walls of different contour tochange the definition of the throat of the nozzle and the divergentsection of the nozzle.
 14. An array of convergent-divergent nozzles asin claim 8 wherein:both said top and bottom walls of each nozzle arecontoured to also define the convergent section of the nozzle.
 15. Anarray of convergent-divergent nozzles as in claim 8 wherein:the array ofnozzle forms the input to an axial turbine rotating about said axis. 16.An array of convergent-divergent nozzles as in claim 15 wherein:thearray of nozzles form the input to a radial turbine.
 17. An array ofconvergent-divergnt nozzles as in claim 16 wherein:said side walls areadjustable.
 18. An array of convergent-divergent nozzles about an axisof a turbine for passage of motive fluid at supersonic speed, each ofsaid nozzles including:a pair of opposed spaced apart side walls; a topwall extending between said side walls; and a bottom wall spaced fromsaid top wall and extending between said side walls; said top and bottomwalls and said said walls cooperating to define a flow passageway; andsaid top and bottom walls being contoured to define at least the throatof the nozzle and the divergent section of the nozzle, said contouringof said top and bottom walls of each nozzle being asymmetric withrespect to said axis and defining a symmetric flow passage between saidtop and bottom walls in the direction of flow downstream of said throat.19. A convergent-divergent nozzle as in claim 18 wherein:said contouringof said top and bottom walls is the major factor in defining saidthroat.
 20. A convergent-divergent nozzle as in claim 18 wherein:saidopposed side walls are regular throughout the major part of theirlength.
 21. A convergent-divergent nozzle as in claim 18 wherein:theangle of said throat with respect to the direction of flow in the nozzledownstream of the throat is a function of the contouring of said top andbottom walls.
 22. A convergent-divergent nozzle as in claim 18wherein:said side walls are of uniform size and shape.
 23. Aconvergent-divergent nozzle as in claim 18 wherein:said top and bottomwalls are contoured to also define the convergent section of the nozzle..Iadd.
 24. An array of convergent-divergent nozzles about an axis of aturbine for passage of motive fluid at supersonic speed, each of saidnozzles including:a pair of opposed spaced apart side walls; a top wallextending between said side walls; and a bottom wall spaced from saidtop wall and extending between said side walls; said top and bottomwalls and said side walls cooperating to define a flow passageway; andsaid top and bottom walls being contoured to define at least the throatof the nozzle and the divergent section of the nozzle, said contouringof said top and bottom walls of each nozzle defining a symmetric flowpassage between said top and bottom walls in the direction of flowdownstream of said throat. .Iaddend. .Iadd.25. A convergent-divergentnozzle as in claim 24 wherein: said contouring of said top and bottomwalls is the major factor in defining said throat. .Iaddend. .Iadd.26. Aconvergent-divergent nozzle as in claim 24 wherein: said side walls areof uniform size and shape. .Iaddend. .Iadd.27. A convergent-divergentnozzle as in claim 24 wherein: said top and bottom walls are contouredto also define the convergent section of the nozzle. .Iaddend. .Iadd.28.An array of convergent-divergent nozzles about an axis of a turbine forpassage of motive fluid at supersonic speed, each of said nozzlesincluding:a pair of opposed spaced apart side walls; an outer wallextending between said side walls; and an inner wall spaced from saidtop wall and extending between said side walls; said outer and innerwalls and said side walls cooperating to define a flow passageway; andsaid outer and inner walls being contoured to define at least the throatof the nozzle and the divergent section of the nozzle, said contouringof said outer and inner walls of each nozzle defining a symmetric flowpassage between said top and bottom walls in the direction of flowdownstream of said throat. .Iaddend. .Iadd.29. A convergent-divergentnozzle as in claim 28 wherein: said contouring of said outer and innerwalls is the major factor in defining said throat. .Iaddend. .Iadd.30. Aconvergent-divergent nozzle as in claim 28 wherein: said side walls areof uniform size and shape. .Iaddend. .Iadd.31. A convergent-divergentnozzle as in claim 28 wherein: said top and bottom walls are contouredto also define the convergent section of the nozzle. .Iaddend.